Area Forecast Discussion
Issued by NWS Medford, OR

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000 FXUS66 KMFR 210111 AFDMFR Area Forecast Discussion National Weather Service Medford OR 611 PM PDT Tue Apr 20 2021 .UPDATE...Updated the aviation section. && .AVIATION...For the 21/00Z TAF Cycle...VFR ceilings and a few showers will linger in northern California this evening. Also, LIFR/IFR ceilings and visibilities cover most of the coast north of Cape Blanco. This coastal stratus is expected to expand along the coast and in to the Coquille Valley overnight. It will then burn off back to the beaches during the morning with lingering IFR again expected Wednesday afternoon north of Cape Blanco. Elsewhere, VFR conditions are expected through Wednesday evening. -DW && .MARINE...Updated 200 PM PDT Tuesday 20 Apr 2021...A thermal trough near the coast will support strong north winds through Wednesday, especially south of Cape Blanco. Winds and seas will continue to increase into the evening, with hazardous seas developing beyond 5 NM from shore and south of Port Orford. Very steep and hazardous seas are expected again Wednesday afternoon. Winds will ease some Thursday into Friday, but steep seas will linger through Thursday evening. Winds will become southerly Saturday, when the first in a series of fronts will move onshore. -Sven && .PREV DISCUSSION... /Issued 218 PM PDT Tue Apr 20 2021/ DISCUSSION...The latest radar image shows isolated a line of showers (likely from a deformation zone) aligned from west to east in southern Jackson and Klamath county. Additionally, showers are also confined to northern California. Over time, the line of showers in the above mentioned areas will continue to move south into California with decreasing cloud cover. Meanwhile mainly isolated showers will continue through this afternoon in northern California. This is all due to a weak upper low located along the California/Oregon border, what is bringing a weak trigger and cooler air aloft. The combination of the two will bring enough instability to generate additional isolated showers and a isolated storm or two this afternoon. Any leftover isolated showers and storms will end early this evening with dry weather expected tonight with clearing skies for most of the area. The exception will be along the coast from about Cape Blanco north where marine stratus is expected to return. The marine stratus could push inland into the Coquille Basin, but that should be the extent of it. Elsewhere it will be clear. After today, were back to dry and warm weather until the end of the week. A weak disturbance within a northwest flow will move through late Wednesday night with the main effect being an increased onshore flow. Therefore, we can expect marine stratus to make it`s way further inland to include most, if not the entire Umpqua Basin by Thursday morning. Friday will be dry as a ridge axis moves overhead. This will quickly move east Friday evening as an upper trough approaches from the southwest. The evidence is pretty solid we`ll get our first measurable rainfall in our forecast area this morning, starting at the coast later Friday evening, then pushing inland mainly west of the Cascades Friday night. -Petrucelli Extended discussion...Sat 24 Apr through Tue 27 Apr 2021. The overall pattern will change to a much wetter regime in the extended period. The offshore long wave ridge which brought the dry weather to the area will break down and move onshore Friday. This will open the storm door and the upstream upper trough will move onshore Sunday night. Short waves ejecting from the trough will push a series of fronts onshore beginning Friday night. Sunday looks to be the wettest day overall. The trough will move out to the east Monday and a weak ridge will build into the west coast. This looks to be a dirty ridge; short waves moving over the top of it will continue to support frontal activity that will bring more precipitation to the area. A significant front will move onshore Tuesday. The ridge will break to the east of the area Tuesday, but it will build over the intermountain states as the upstream trough deepens offshore. Eventually there will be a break in the action, but the deterministic models and their ensembles indicate that this won`t happen until next Thursday. The 8 to 14 day outlook, valid Wed 28 Apr to Tue 04 May, shows greater chances for above normal temperatures and above normal precipitation for southern Oregon, and greater chances for above normal temperatures and near normal precipitation for northern California. FIRE WEATHER...Updated 300 PM PDT Tue 20 Apr 2021...As evidenced by the 1400+ acre wildfire (Ponina) that ignited near Beatty/Bly yesterday, early spring dryness has led to abnormally dry fuel conditions area wide, but especially across the east side. Contacts with local fuels officials today indicated moderate fire danger over portions of the west side and in most of NorCal, while FWZs 624/625 below 5000 feet in Oregon and FWZ 285 in California all indicated high fire danger. High pressure will build in tonight, initiating a warming and drying trend that will continue into Friday evening. It will also be breezy in the afternoons and evenings, especially Thursday. This could bring borderline Red Flag conditions to portions of the east side. A cooler and much wetter pattern will initiate Friday night as the first of several systems moves onshore. At this time it looks like this pattern will persist through at least the middle of next week. && .MFR WATCHES/WARNINGS/ADVISORIES... OR... CA...None. Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Thursday for PZZ350-356-370-376. Hazardous Seas Warning until 11 AM PDT Thursday for PZZ356-376. $$ MAP/DW/BMS

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